1. Field of the Invention
The present invention relates to an oscillometric type blood pressure measurement device, a blood pressure measurement method and a blood pressure measurement program.
2. Description of the Related Art
An oscillometric type blood pressure measurement device as a device that automatically measures a blood pressure value of a living body is known (refer to Japanese Unexamined Patent Application No. H09-253059, Japanese Unexamined Patent Application No. H03-55026, and Japanese Unexamined Patent Application No. 2002-209859.)
An oscillometric type automated blood pressure measurement device gradually changes a compression on a living body through a cuff wrapped around one part of the living body at a predetermined pace and, at the same time, detects cuff pressure during a period of this change in compression. Then, from the detected cuff pressure, the oscillometric type automated blood pressure measurement device detects a pulse wave that is a pressure component synchronized with a pulse of the living body and superimposed on the compression, and determines the blood pressure value of the living body based on a change in amplitude of that pulse wave.
FIG. 10 is a diagram illustrating a change in detected cuff pressure in a period where the cuff is being inflated by a basic oscillometric type blood pressure measurement device. In FIG. 10, a horizontal axis represents time and a vertical axis represents detected cuff pressure.
A straight line illustrated by a broken line of FIG. 10 illustrates compression from the cuff (inflation base line), and the example of FIG. 10 illustrates a case where compression is increasing at a constant pace from the cuff inflation start. A solid line of FIG. 10 illustrating each mountain-shaped wave form is illustrating a pulse wave superimposed on the compression illustrated by a broken line.
Various ways are known for calculating an amplitude value of a pulse wave needed to determine a blood pressure value. For example, in FIG. 10, if a difference between a peak value of the pulse wave and the pressure, on a straight line connecting rising points of the pulse wave, at a time when the peak value is obtained (a1, a2 and a3 in FIG. 10) is calculated as a pulse wave amplitude, the blood pressure value can be determined with high accuracy.
The blood pressure measurement devices disclosed in the Japanese Unexamined Patent Applications do not obtain amplitude value by the aforementioned method, but they do perform a variety of innovations to raise a measurement accuracy of the blood pressure value.
The blood pressure measurement device of Japanese Unexamined Patent Application No. H09-253059 measures a change pace of a compression of the cuff at a time of pulse wave generation and raises the measurement accuracy of the blood pressure value by correcting the compression at the time of pulse wave generation according to this pace.
The blood pressure measurement device of Japanese Unexamined Patent Application No. H03-55026 raises the measurement accuracy of the blood pressure value by correcting an error in the blood pressure value that is subject to a pulse rate.
The blood pressure measurement device of Japanese Unexamined Patent Application No. 2002-209859 raises the measurement accuracy of the blood pressure value by correcting pulse wave amplitude based on a photoelectric pulse wave detected from a photoelectric pulse wave sensor, correcting the compression based on a heartbeat period and determining maximum and minimum blood pressure values from post-correction pulse wave amplitude and pressure.
Control to increase a compression from a cuff at a constant pace is performed in an oscillometric type blood pressure measurement device in order to detect an amplitude value of a pulse wave with precision, as illustrated in FIG. 10.
Sphygmomanometers for home use have become more prevalent in recent years, but from a perspective of improving usability of sphygmomanometers for home use, miniaturization and cost reduction are demanded. Because of that, cost reduction and miniaturization of a pump that sends fluid to a cuff have advanced.
However, because pump size and cost have a mutual trade off relationship with output flow rate, it becomes increasingly difficult to achieve a desired inflation pace as miniaturization and cost reduction advance.
FIG. 11 illustrates a state where a change pace of the compression in FIG. 10 changes in midstream. FIG. 11 illustrates a state of a time when the change pace of the compression of the cuff up to time t1 and the change pace of the compression of the cuff after time t2 change.
In this state, the compression of the cuff between time t1 and time t2 changes to a curved condition as shown by a dashed line, and the compression of the cuff is not changing in a constant manner. Accordingly, when amplitude a2 of the pulse wave is determined through the aforementioned method, an error is generated in relation to a precise amplitude a2′, and measuring accuracy of a blood pressure value decreases.
The blood pressure measurement devices disclosed in Patent Documents 1-3 do not calculate a difference between a peak value of the pulse wave and a pressure, on a straight line connecting rising points of the pulse wave, at a time when the peak value is obtained as a pulse wave amplitude value. Because of that, a situation where the compression of the cuff is not changing in a constant manner does not occur with Patent Documents 1-3 and, not surprisingly, this situation is not considered in Patent Documents 1-3.
Accordingly, one or more embodiments of the present invention provides a blood pressure measurement device, a blood pressure measurement method and a blood pressure measurement program that are capable of performing measurement of blood pressure value with high accuracy.